The present invention relates to torque transmitting fluid couplings, and more particularly, to such couplings which utilize internal, temperature-responsive valving to control the flow of fluid within the fluid coupling.
Fluid couplings of the type to which the present invention relates are well known in the art and may be better understood by reference to U. S. Pat. Nos. 3,055,473; 3,174,600; and 3,339,689, assigned to the assignee of the present invention. Briefly, such fluid couplings typically include a coupling body and a cover which cooperate to define a fluid chamber, and a valve plate dividing the fluid chamber into a fluid operating chamber and a fluid reservoir chamber. A coupling member is disposed within the fluid operating chamber and is rotatable relative to the coupling body, the body and member each including a plurality of concentric annular lands alternately positioned such that rotation of the coupling member causes the viscous fluid in the operating chamber (and between the lands) to exert a viscous drag on the coupling body, thereby rotating the body. The valve plate defines a fill orifice and a discharge orifice communicating between the operating chamber and the reservoir chamber. Some form of temperature-responsive valving arrangement controls the flow of fluid through the fill and discharge orifices, such that the amount of fluid in the operating chamber increases when the temperature increases and decreases when the temperature decreases.
It is well known in the art, as shown in U. S. Pat. No. 3,613,847 to utilize a single temperature-responsive valve member to control, generally simultaneously, the flow areas of both the fill and discharge orifices. This arrangement may be generally advantageous because, under increasing temperature conditions, the flow area of the discharge orifice is reduced as the flow area of the fill orifice is increasing, thus permitting a more rapid increase in the volume of fluid in the operating chamber, resulting in a more rapid rise in the output speed of the coupling device.
Therefore, although the utilization of the present invention requires only that a valve member be used to vary the flow area of the discharge orifice, it is more probable that the invention would be used in the environment described above, i.e., where a single valve member controls the flow areas of both the fill and discharge orifices, simultaneously, and therefore, the invention will be described in connection therewith.
A problem which has arisen in connection with the use of the valving arrangement described above is what is frequently referred to as "blowoff," i.e., the tendency for the valve member to be blown or moved away from the valve plate by the flow of fluid from the operating chamber through the discharge orifice. This is especially likely to occur in situations in which, except for the valve member covering the discharge orifice, the result would be "high-speed pump out," i.e., the tendency for fluid to be pumped out the discharge orifice at a faster rate than it enters the fill orifice at high input speeds.
Prior attempts to solve this problem have generally centered around the valve member itself. For example, the valve member has been made thicker in an attempt to increase the rigidity and decrease the tendency for the valve to deflect away from the valve plate. This solution has been generally satisfactory in certain larger coupling devices wherein the temperature-responsive means utilized to control the valve position is capable of exerting sufficient torque to overcome the increased weight of the valve member, as well as the frictional forces associated with the movement of the valve member.
However, in the majority of the fluid coupling devices used for automotive accessories such as radiator fans, the temperature-responsive means, typically a bimetal coil, is capable of exerting only a relatively small torque on the valve member (such as 1.0 inch-ounces per degree of angular deflection of the valve member.) It has been found that such a torque output capability on the part of the bimetal coil dictates a very thin, light valve member, typically, in the range of about 0.005 to 0.010 inches (0.127 to 0.254 mm). Therefore, although the present invention may be utilized with fluid coupling devices in which the valve member is selected from any one of a number of configurations and sizes, it is especially advantageous when used with a generally flat, thin valve member having approximately the above-mentioned thickness, and will be described in connection therewith.